Run the container as a user without privileges

[alphastorm]

Currently the client runs as root by default:

user@host:~/keep-core$ sudo docker run --entrypoint "" keepnetwork/keep-client:latest whoami
root

Per https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#user it's better to run as a non-root user when possible. This copies the approach from https://github.com/prometheus/prometheus/pull/2859, which defaults to using nobody and allows overrides using the --user flag (for more discussion see https://github.com/prometheus/prometheus/issues/3441).

After the change:

user@host:~/keep-core$ sudo docker run --entrypoint "" keep-client-nobody:latest whoami
nobody

Tested by building the image from source and running my testnet node with it and the --user $UID:$GID flag (node was originally setup using these instructions).

NOTE: This is a breaking change and after landing users will need to ensure the mounted persistent directory has the correct ownership and/or they set --user correctly.

[mhluongo]

@nkuba thoughts on this?

[nkuba]

I'm OK with the change but I'd like to confirm it won't break our test environments first.

EDIT: Actually there's a high probability this will break our envs. We need to reflect this change in env configurations and merge it once the environment is ready to handle it.